By virtue of the technical improvement and increased requirement of consumer electrics with image processing functions, such as digital cameras, scanners or smart phones, the demand for image sensors is continually growing.
Generally, image sensors can be divided into two types, front-side illuminated image sensors and backside illuminated image sensors.
Since the sensor array of a front-side illuminated image sensor is disposed on the front side of a semiconductor substrate, over which a plurality of inter-metal layers are formed, the incident light entering the image sensor must pass through gaps in the inner-metal layers, and the light is obstructed by the inner-metal layers and cannot be delivered efficiently to the sensor array, thus the quanta efficiency of the front-side illuminated image sensor can be inversed effected.
In comparison to a front-side illuminated image sensor, the incident light of a backside illuminated image sensor is arranged to entering the image sensor through the backside of the substrate rather than passing through the inner-metal layers, such that most of the incident light can be delivered to the sensor array without any obstruction. Thus the quanta efficiency of the backside illuminated image sensor is significantly better than that of the front-side illuminated image sensor.
However, fabricating a backside illuminated image sensor requires additional procedures in contrast to fabricating a front-side illuminated image sensor. For example, fabricating a backside illuminated image sensor requires a substrate thinning procedure after a handle wafer is bound on the front side of the inner-metal layers. Besides, the existence of the handle wafer may obstruct the subsequent packaging process from making the wiring bond pad of the inner-metal layer, thus some additional through silicon vias (TSV) may be needed. Accordingly, fabricating a backside illuminated image sensor is more complicated and costly than fabricating a front-side illuminated image sensor.
Currently, an improved technology has been adopted by those skilled in the art, wherein an essential color filter associated with lens is embedded in a front-side illuminated image sensor by the conventional lithography process in order to reduce the optical path and improve the quanta efficiency of the front-side illuminated image sensor, thus the front-side illuminated image sensor can provide an optical performance substantially similar to that of a backside illuminated image sensor.
However, since the rough and unevenness surface of the embedded color filter may adversely affect the subsequent process and yield, thus the embedding depth of the color filter may be limited. These problems may get worse, as the current front-side illuminated image sensor is required to provide more and more resolution and small pixel size.
Therefore, it is necessary to provide an improved optical microstructure with a stand-alone color filter associated with micro lens to manufacture an image sensor with higher quanta efficiency and lower manufacturing cost, and to improve the long existing cross-talk problems.